Conventional I.V. catheters have been used for years to provide direct access to a patient's veins for administration of intravenous solutions and medications. FIG. 9 shows a currently used design for catheters which includes a catheter-needle complex composed of two main units, the catheter 8A and the needle 7A, each affixed to their hubs 10A and 5A, respectively. The hubs of the two units are connected together in a snug male-female type orientation. During insertion into a patient's vein, the I.V. catheter assembly is held by the rear portion of the needle hub 3A in FIG. 9 with the needle in the "bevel up" position. The needle is advanced (with the two units still joined) through the skin of the patient aiming directly at the vein for entrance into the vein lumen. Entry into the vein will be confirmed when a flashback of blood is seen in the translucent flashback chamber 2A in FIG. 9.
Once the flashback of blood is seen, the needle hub unit 5A is then held stable while the catheter is advanced into the vein by sliding it over the needle in a forward axial motion. (Some recommend slight advancement of the entire unit after the flashback of blood is seen to insure that the needle tip is entirely in the vein lumen before the catheter is advanced.) After the catheter is advanced into the vein, the needle is removed and a tubing adaptor (shown in FIGS. 11 and 12) is connected for administration of fluids. The tubing adaptor has a slightly tapered configuration (see 15 in FIGS. 11 and 12) and is held in place by its very snug fit into the tapered inner channel of the catheter hub 9A in FIG. 9. To provide a more secure connection, some manufacturers have incorporated an external luer lock device on the tubing adaptor (see 17 in FIG. 12).
There are several manufacturers of the above-described I.V. catheter each with their own subtle differences in sizes, shapes, and materials. However, they all conform to the same basic design and are advanced into the vein in similar fashion, namely, by sliding the catheter over the needle in a forward axial motion. In considering all operators placing I.V. catheters and all patients receiving them, one would estimate that at best only 50-60% of the time these catheters are successfully inserted on the first attempt. The other 40-50% of these operations require a second or even a third, fourth, or even fifth attempt, thereby causing excessive pain and contusions to the patient and frustration to the operator.
There are several reasons for the low success rate of insertion of a conventional I.V. catheter on the first attempt. First, the needle may not enter the vein. This is frequently due to very tough skin, "rolling," small or thrombosed veins, or just poor "aim." These difficulties can often be overcome with more thorough evaluation of the vein and puncture site and better technique. A much more frequently encountered problem is when the needle does enter the vein (and a flashback of blood is seen in the flashback chamber), but the catheter, which is made of coated plastic material, will not advance and often buckles or kinks upon sliding forward axially. This situation requires a new catheter and puncture. The resistance to the entry of the catheter usually occurs within the first 1-6 mm of advancement. Several explanations can be given for this problem. First and foremost is the fact that the sharp needle tip is a separate unit from the relatively blunt tapered catheter tip (see needle tip 7A and catheter tip 8A in FIG. 10). The distal catheter must slide axially over the needle through tissues that the sharp needle tip has already traversed. The intervening tissues offer resistance for the catheter tip and shaft. Even when both tips are in the lumen of the vein, the catheter may not advance smoothly because of resistance from the surrounding tissue during the axial sliding motion. A second cause of awkward advancement is related to the "snug" fit design of the male hub component of the needle to the female hub component of the catheter. As the two units are separated when advancing the catheter, there is a subtle recoil of the needle unit caused by the abrupt release of this "snug" fit. The extent of this recoil varies among the different manufactured catheters, depending on the types of material, size of catheter, and the fit. This subtle recoil, which an operator may not even be aware of unless he or she is instructed to consciously take note of it, results in an uneven, non-uniform advancement. In addition, the recoil can cause a minute backward displacement of the needle tip from its desired position in the vein. An additional, but less common, occurrence arises when the puncture site is at or near a vein valve location. Advancement in such a situation may be hindered by resistance from the vein valve.
Manufacturers have attempted to overcome the above deficiencies regarding the use of conventional I.V. catheters by utilizing more advanced, frictionless, and/or less rigid materials. However, although reduced slightly, these problems still exist.
The present invention solves the above-discussed problems by providing catheter assemblies in which rotational movement is integrated into the axial movement of the catheter component during insertion into the patient. In accordance with the invention, forward axial movement of the catheter component can only be achieved by rotation of the catheter component. This integration of the rotational and axial movements of the catheter component overcomes or diminishes the friction forces and other resistance to the penetration of the intervening tissues (e.g., skin, vein walls, etc.) during insertion of the catheter component. The invention also eliminates the recoil phenomenon experienced with conventional catheters during separation and advancement of the catheter components, thus making possible a smoother, more uniform insertion. In addition, the assemblies of the invention permit precise and minute movement control between the catheter and needle components which ensures proper positioning in the vein. The invention results in a more efficient and reliable insertion and a significantly higher percentage of successful placements on the first attempt. Consequently, by using the present invention, there will be fewer puncture attempts, less trauma to the veins, and less contusions. Moreover, the invention standardizes the insertion procedure of catheters which significantly aids in the training of medical personnel.